[move-only] Do not box captures if the capturing closure is no escape.

Thanks to JoeG for seeing this quickly and preventing me from having to track
this down!

Author: gottesmm

lib/SIL/IR/TypeLowering.cpp

@@ -116,10 +116,11 @@ CaptureKind TypeConverter::getDeclCaptureKind(CapturedValue capture,
       var->getType(), TypeExpansionContext::noOpaqueTypeArchetypesSubstitution(
                           expansion.getResilienceExpansion()));
 
-  // If this is a noncopyable 'let' constant that is not a shared paramdecl,
-  // then we know it is boxed and want to pass it in its boxed form so we can
-  // obey Swift's capture reference semantics.
-  if (!var->supportsMutation() && lowering.getLoweredType().isPureMoveOnly()) {
+  // If this is a noncopyable 'let' constant that is not a shared paramdecl or
+  // used by a noescape capture, then we know it is boxed and want to pass it in
+  // its boxed form so we can obey Swift's capture reference semantics.
+  if (!var->supportsMutation() && lowering.getLoweredType().isPureMoveOnly() &&
+      !capture.isNoEscape()) {
       auto *param = dyn_cast<ParamDecl>(var);
       if (!param || param->getValueOwnership() != ValueOwnership::Shared) {
         return CaptureKind::ImmutableBox;

test/SILOptimizer/moveonly_nonescaping_closures.swift

@@ -46,21 +46,22 @@ func a(x: __shared M) {
     borrow(x)
 }
 
-func b(x: __owned M) {
+func b(x: __owned M) { // expected-error {{'x' used after consume}}
     clodger({ borrow(x) }, consume: x)
-    // expected-error @-1 {{'x' was consumed but it is illegal to consume a noncopyable immutable capture of an escaping closure. One can only read from it}}
+    // expected-note @-1:25 {{non-consuming use here}}
+    // expected-note @-2:37 {{consuming use here}}
 }
 
 func c(x: __owned M) {
     clodger({ borrow(x) })
     borrow(x)
     consume(x)
-    // expected-error @-1 {{'x' was consumed but it is illegal to consume a noncopyable immutable capture of an escaping closure. One can only read from it}}
 }
 
-func d(x: __owned M) {
+func d(x: __owned M) { // expected-error {{'x' consumed in closure. This is illegal since if the closure is invoked more than once the binding will be uninitialized on later invocations}}
     clodger({ consume(x) })
-    // expected-error @-1 {{'x' was consumed but it is illegal to consume a noncopyable immutable capture of an escaping closure. One can only read from it}}
+    // expected-error @-1 {{copy of noncopyable typed value. This is a compiler bug. Please file a bug with a small example of the bug}}
+    // expected-note @-2 {{consuming use here}}
 }
 
 func e(x: inout M) {